Neuroleptic drugs are the most efficacious treatment for schizophrenia. However, their long-term use can lead to an extrapyramidal complication called tardive dyskinesia for which there is currently no effective treatment. Efforts are, therefore, toward prevention of the disorder by identifying patients who are at most risk. Five years ago we carried out an epidemiological study of tardive dyskinesia in 261 schizophrenic outpatients undergoing long-term maintenance treatment with neuroleptics. The prevalence of the disorder was 31% and stepwise multiple logistic regression analysis revealed that the principal variables related to its incidence were age, long records of hospitalization, poor therapeutic response, fluphenazine treatment and few parkinsonian symptoms. We propose to carry out a follow-up study of these patients who have since been maintained on neuroleptic therapy in a special follow-up clinic of which the principal applicant is the psychiatrist-in-charge. The pharmacotherapy in the clinic has been under strict control and the policy has been to reduce the dosage to the minimum therapeutic level and to avoid polypharmacy. The same neurologist as before will evaluate the patients' extrapyramidal symptoms using specially designed scales and the same psychiatrist will evaluate the patients' psychiatric symptoms, prognosis and any signs of tardive psychosis that occurred during dosage reduction. Multivariate statistical analysis will be used to identify variables that are related to the course of tardive dyskinesia during the 5-year period. In addition the entire present population of the clinic will be surveyed and a similar analysis carried out to search for factors related to the current incidence and severity of the disorder. This is the first long-term follow-up of tardive dyskinesia and the first study of the disorder in a population in which the medication has been under strict control. The work is of direct relevance to the treatment of schizophrenic patients and may lead to guidelines that will assist in the prevention and alleviation of tardive dyskinesia.